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View Full Version : Help. Spot burn on the stator winding







Peterjon
19-08-2014, 04:49 PM
Hi. Advice please gentlemen.

Had a spot burn on a semi compressor (Bock HGX34P/215-4 S ) stator winding. Took the stator for re winding. When I tried to refit the stator to the crank side the windings were sticking out too far and would not fit. Back to re winders who heated up the casing to get the windings to go in more. Better but still would not fit. Back to re winders who put the stator back in the oven to soften the winding resin to mould them deeper into the casing.
Re fitted. Replaced oil sep. Fitted a double core burn out drier. Vacuum and re gas. Did an oil change. Oil pickup sieve perfectly clean. Sieve on suction inlet to compressor. Flushed out suction accumulator. Switched on Friday evening. Checked amps and voltage all good. Monday morning compressor tripped on manual motor starter/overload. Found another spot burn on the winding. Re winders say I had contamination. As in a small piece of metal got in with the windings and shorted.

My argument is if that were the case it would have lasted longer than a few hours. And the cause was perhaps at a join in the winding or the re winder not been careful enough with all their playing around to get the windings deeper into the casing.

Your opinions will be appreciated.

PRESS
19-08-2014, 06:10 PM
My gut is telling me that your rewinder is trying to pull wool out of your ears. there might be something else though you might have missed which cased the original winding to burn. sport burns are usually caused by what your rewinder told you. Is compressor reconditioning a usual thing which you do often?

Peterjon
19-08-2014, 06:28 PM
The original burn I was told was from lightning. But I didn't get to see it. I believe lightning causes a bigger blow than what I am seeing now. This is a very small spot. Could a damaged supply cable cause a spot burn? Surely I would have picked it up on my amp tester or seen voltage irregularities?

I have done a few overhauls. But usually go with a new compressor as the cost of an overhaul doesn't seem to be worth it sometimes. (for the sizes I deal with)

This is the first time I am using these rewinders.

I'm going to check the cables with a mega, fit fuses and a over/under voltage protection to the supply. But what else can I do? Cant afford another burn.

al
19-08-2014, 10:44 PM
might be safer to fit a suction drier to rule out system damage, bad rewinding would definitely short but so too could metal or acid in system, did you meggar the winding before turning it on?

GHAZ
20-08-2014, 12:11 AM
Hi if the projection of the stator was to big, the softening process and bashing it too size can cause damage, e.g. The insulation on wires can come off and it starts arcing. Eventually a blow out, and in or near the slot it causes spot burn.

Peterjon
20-08-2014, 08:09 AM
Thank you. Al i do have a double core suction/burnout drier to prevent anything coming back to the compressor. Plus the compressor is fitted with a good quality sieve on the suction inlet to the compressor.

I did not mega the windings. i just used my ohm meter on my multi meter as a quick double check.

Surely if it were metal contamination it would have lasted a bit longer than a day or two? How long would the winding last with metal contamination?

Kind Regards

Peterjon.

Rob White
20-08-2014, 08:44 AM
Hi if the projection of the stator was to big, the softening process and bashing it too size can cause damage, e.g. The insulation on wires can come off and it starts arcing. Eventually a blow out, and in or near the slot it causes spot burn.

I agree, heating up, cooling down and trying to get
it to fit into something that is too small, would have
stressed the thing. The insulation on the winding wires
is only glorified varnish and if there was a weak point
all that stress won't help.

Rob

.

Peter_1
20-08-2014, 09:25 PM
Think Rob White is 'spot' on. Sorry.

Peterjon
21-08-2014, 01:38 PM
Thank you everyone!

Peterjon.